Concentration of extracts by freezing



July 4, 1967 s'VANoE CONCENTRATION OF EXTRACTS BY FREEZING OriginalFiled July 25. 1963 I FIG. I.

PRUDUC T F/azz: I

FIG. F4.

IN V EN TOR.

HANS SVANOE United States Patent 3,328,972 CONCENTRATION OF EXTRACTS BYFREEZING Hans Svanoe, Warren, Pa., assignor to Struthers Scientific andInternational Corporation, New York, N.Y., a corporation of DelawareContinuation of application Ser. No. 297,498, July 25, 1963, now PatentNo. 3,209,378. This application Aug. 9, 1966, Ser. No. 571,358

1 Claim. (Cl. 62123) This application is a continuation-in-part of theHans Svanoe application Ser. No. 235,555, filed Nov. 5, 1962, and acontinuation of application Ser. No. 297,498, filed July 25, 1963, nowPatent No. 3,209,378.

The invention relates to a process for the concentration of comestibleand potable extracts by crystallization and more particularly relates.to freezing aqueous solutions containing flavors to concentratedextracts while removing the water through crystallization.

The prior art describes processes in which the solvent in varioussolutions is frozen and the resulting crystals separated, thus eitherconcentrating the solution or liberating the solvent from the solutionfor subsequent use for food or drink. In carrying out such processes ofthe art, the solution may be placed in contact with a heat transfersurface such, for example, as the external surface of an internallycooled drum which is immersed in the solution to be concentrated, or theinternal heat transfer surface of an externally cooled cylinder. Thesolvents of the solutions, under prescribed conditions, are frozen outof the solutions on the heat transfer surfaces and by one means oranother the frozen solvent scraped from the heat transfer surfaces.Other methods have been disclosed for the removal of solvents bycrystallizations in which particles of an insoluble solid, cooled belowthe freezing point of the solution are continuously introduced into thesolution, the particles incased in the frozen solvent and continuouslyremoved from the solution. Contrariwise droplets of an organicrefrigerant are forced into a solution and the solvent therein frozenout by the latent heat of evaporation, released in situ, of the re--frigerant. After thus removing the frozen solvent and extracting itsheat of crystallization, the particles or droplets are again treated toeffect the freezing of the solvent and the operation repeated.

In the processes of the art such as those described above, efiicientoperation suffers due to the unconscionable amount of the concentratelost in the crystals com-minuted by scraping during removal from theheat transfer surfaces. Heat transfer losses due to the ice coating onthe surfaces are also high. Recovery of the concentrate, occluded orretained on the ice, by washing, extraction, or other means invariablydissolves the small crystals, thus diluting the concentrate and loweringthe yield. The process of the invention obviates these and otherdifliculties and advances the art of concentrating a solute by removingthe solvent by an improved cooling, crystallization, and crystal growthprocess.

Objects of the invention include: an improved process for theconcentration of potable concentrates and for the concentration ofpalatable liquids by a controlled crystallization process; thecrystallization and environmental control of such processes to producedense ice crystals 3 ,328,972 Patented July 4, 1967 from fruit,vegetables, bean, and comesti-ble extracts and the like; the maintenanceof a non-crystallizing refrigeration environment in which to provide thesub-cooling of dilute potable liquids and cornestible extracts and acrystallization environment for the nucleation and growth of crystalsresulting therefrom; the concentration of solutes by freezing and theimproved process of separating concentrated extracts from ice. Otherobjects and advantages of the invention will hereinafter appear.

The invention will be more readily understood by reference to theattached drawings in which like parts have like numbers throughout.

FIG. I represents, diagrammatically and in partial cutaway section, inan elevation view, a crystallizer and crystal growth zone in which theprocess of the invention is conducted.

FIG. II represents, in plan view the form and shape of the agitatorsused in the crystallization zone represented in the elevation of FIG. I.

FIGS. IIIA and B, FIGS. IVA and B and FIGS. VA and B represent inelevation and plan views embodiments of types of agitators that are usedin accordance with the invention.

In a general sense the invention is directed to a process for theconcentration of a solute in a solvent therefor, e.g., a coffee extract,by the removal of the solvent by freezing. A slurry containing a solute,solvent, and crystals of the solvent is circulated in a closed cycle,such as is illustrated in FIG. I or alternatively may be passed througha single crystallizer without recycling or through a plurality ofcrystallizers in series depending on the amount of concentrationdesired. A feed of a dilute solution of the solute is fed into thecirculating slurry. The augmented and diluted slurry is passed through asubcooling zone aid, if desired, a separate crystallization zone of thecycle. The sub-cooling of the dilute solution is effected in a confinedarea, hereinafter referred to as a boundary film, an area that is formedbetween an agitator periphery, and a metal cooling surface, thesubcooling being effected in such a way that the boundary film ismaintained at a temperature below the freezing point of the solutionplaced therein and importantly subjected to sufiicient intensity oftubulence that on the one hand the film of solution is sub-cooled to atemperature below its freezing point and on the other the subcooling ofthe solution is not released in the boundary film as heat ofcrystallization. The sub-cooling on the contrary is released as the heatof crystallization outside the boundary film, as crystals of the solventtnd as crystal growth. The dilute solvent feed is continuouslyintroduced into the crystallization zone, the solvent concentrated bycrystal growth and the concentrated extract removed.

An embodiment of the invention constitutes passing the dilute solutioninto an apparatus, such as that illustrated in FIG. I, through inlet 1and into the circulating slurry of the solution and crystals thereofflowing in conduit 9. The slurry contains a solution (of the extract tobe concentrated), the solute and crystals of the solvent. The slurrypasses into zone 2 then into the heat exchanger (referred to morespecifically below) and crystallizer 3 and pump 4, the latter forcingthe slurry continuously through the crystallizer at a desired velocity.A propeller shaft 5 is centered in crystallizer 3 to which are fixedagitators 6. As the slurry with its load of feed passes intocrystallizer 3 it meets the slurry therein which is in a state ofturbulence. Agitators 6 are so constructed and arranged and are sorotated and also so propelled in vertical directions by propeller shaftthat the boundary film, i.e., the layer of liquid proximate to theinside wall of the crystallizer is in a state of turbulence which Willbe more fully p'articularized hereinafter. Between the outer wall of thecrystallizer 7 and the flowing slurry is a heat transfer surface 8. Afluid refrigerant or a film of an evaporating refrigerant of anysuitable kind flows at a sufficient temperature to refrigerate (byindirect heat exchange) and sub-cool the solvents in the film, i.e.,lower the temperature below the freezing point of the solution in thefilm. The removal of the heat of crystallization and the removal of thenecessary heat to maintain the temperature of the slurry at the properfreezing temperature is carried by the sub-cooled solvent to zone 12. Aslurry containing, inter alia, the concentrated solution is withdrawnfrom crystallizer 3 through outlet 10, the crystal content separatedtherefrom and the concentrate sent to storage.

An important feature of the invention is the creation of and maintenanceof the boundary film. It is well known (cf. Principles of Chem. Eng.,Walker, Lewis and McAdams, 1923, p. 134) that When a liquid is incontact with a solid there is strong evidence to show the presence of anadhering relatively stationary film of fluid on the surface of thesolid, 2. film that becomes thinner as the velocity of the fluidparallel to the surface increases, but which breaks away from the solidonly at very high velocities, if at all. Applicant has found that duringthe concentration of a solution by freezing by prior art processescrystals are generated in the stationary film. If, he reasoned, crystalgeneration could be prevented while at the same time the solution beproperly refrigerated by indirect heat exchange, many of thedifficulties encountered by the prior art should be eliminated. Byextensive research crystal generation has been eliminated in the filmand the crystallization transferred to the crystallization and crystalgrowing zones from which the crystals can easily be withdrawn.Contrariwise the crude and awkward mechanical means of the artinvariably require the use of scrapers or other means of removing thecrystals from the heat transfer surfaces to which they are prone toadhere so tenaciously. The resulting comminution of the crystals by thescrapers occludes the solution being concentrated. Frequent completefreeze up of apparatus used in the art points up, with the difiicultiesdescribed supra, the problems the process of the invention avoids.

Alexander Findley states in The Phase Rule (9th ed., Dover Pub., p. 45),It is a matter of everyday experience that crystallization can beinduced by scratching the inside of the containing vessel with a glassrod. While, therefore, scrapers remove the crystals from the walls, theycontinuously produce more and more loci at which crystals will form onthe heat exchange surfaces thus greatly increasing the problem. Theprocess and apparatus of the invention avoids such multifariouschain-like duplication of crystallization on the heat transfer surfaceswhere no such crystallization can be tolerated.

In accordance with the invention, means are provided to subject theboundary film to sub-cooling and to intense turbulence that prevents theformation of crystals on the heat exchange surface although normallycrystallization would occur with or without scraping under suchsub-cooling. Agitators are provided in the crystallization zone theperiphery of each is surrounded by and defines the inner limits of theboundary zone. The O.D. of the boundary zone is defined by the ID. ofthe heat transfer surface. The agitators whip into and disturb thecontinuity of the film of the boundary zone without touching the heatexchange surface.

In a broad sense one feature of the invention comprises a process ofcontinuously introducing a dilute extract, undercooled below itsfreezing point and within the metastable state, into a concentratingextract and ice slurry, releasing the undercooling to heat ofcrystallization in growth of ice on the crystals present in the slurryand thereby concentrating the extract. The water in the extract ischanged from a liquid phase solvent to a solid phase non-solvent bygrowth of ice on the ice crystals present in the slurry, thus expandingthe size of the crystals and concentrating the extract. By maintainingcarefully controlled conditions during the heat transfer andundercooling, dense pure ice crystals are formed without occlusion ofthe solute. Moreover, the solute retained on the surface of the crystalscan be readily washed from the crystals after their separation from theconcentrated extract.

Any suitable type of agitator or equivalent propellerlike device may beused to create turbulence in the boundary film such, for example, as thepropellers of the drawings. The propeller of FIG. I (and FIG. II), fitssnugly in the crystallizer with a free clearance between its peripheryand the I.D. heat exchanger surface. The clearance should be adjustedwith the rpm. and the vertical up and down strokes of propeller shaft 5in order to provide turbulence in the total boundary film on the heatexchange surface. With the propeller illustrated in FIG. I a clearanceof less than 0.1 inch is adequate when the agitators of FIG. V are usedand given a partial rotation of 120 clockwise and then 120 counterclockwise, the full cycle being repeated 50 to 100 times per minute.When these or the other agitators described in the drawing are used withvertical strokes combined with partial or complete rotation with orwithout reversal deposition of crystals is completely inhibited.

The type of solution being concentrated should also be taken intoconsideration together with its viscosity when determining the amount ofturbulence. The above operations will provide turbulence adequate forconcentrating, for example, a 10% to 35% coffee extract. With a moreconcentrated solution, increase in turbulence is recommended and with amore dilute solution a decrease in the turbulence. As a consequence thepropeller shaft is COntrolled by variable speed motors or like device,not shown in the drawings, which can be adjusted to accomplish thedesired rpm. and speed of stroke. Moreover, it has been found that themore violent turbulence is mostly a matter of power economy. Accordinglywhen starting up a high degree of turbulence is used to avoid allpossibility of crystal formation on the heat transfer surfaces.Thereafter the turbulence may be gradually reduced to conserve powerconsumption, down to a safe/non-crystal forming turbulence.

FIG. III represents, by elevation and plan views, another type ofpropeller. The ribbon-like blade 11 may be segmented or may extendcontinuously from the top to the bottom of the crystallizer. Thepropellers and the angular setting of the blades in FIGS. III and IV arebut examples of propellers and their angulation that may be used in theprocess of the invention. The plan views of FIGS. III, IV, and V aretaken from the dotted positions indicated on the elevations.

The following examples illustrate specific embodiments of the inventionin which parts are by weight unless otherwise noted:

EXAMPLE I A coffee brew containing 10% of coffee cooled to around 0 C.is passed into a slurry flowing in an apparatus such as that illustratedby FIG. I. The slurry in conduit 9 contains from about 12% to less thanabout 15% coffee in an aqueous solution and also from about 15% to about35% ice crystals. Heat transfer surface is provided in the crystallizer,to the extent of to 300 square feet per 1,000 pounds of ice crystals tobe formed from the brew per hour. Refrigerating brine is passed throughthe crystallizer cooling jacket to establish a crystal formingtemperature of not more than about 1 C. below the freezing point of thebrew. The 0D. of each propeller is 0.2" less than the ID. of the heatexchange surface thus giving an annulus boundary lay zone having an r-requal to 0.1 inch. The propeller shaft is rotated at from 30 to 100 rpm.and given an up and down stroke, of at least the distance between thepropellers, at a rate of 2 or more per minute. Slurry is bled from thecrystallizer. Coffee extract concentrated to about 15% is separated fromthe ice crystals in the slurry by centrifuging and either sent tostorage or to another crystallizer .to further concentrate the extract.The ice crystals are washed with cool water or dilute coffee extract andthe wash water returned to the cycle.

EXAMPLE II Coffee extract is concentrated from to about 45% in from 3 to6 stages depending on the size of capacity of the installation. In thefirst stage a 10% coffee solution is concentrated to in accord, exceptfor the recycle means, with the process of Example I. The centrifuged15% coffee extract slurried with to 40% ice are passed into and througha second stage and subjected to similar boundary film sub-cooling andcrystallization in the central zone of the second crystallizer andconcentrated to about 20%. In like manner the extract is concentrated inthe desired number of incremental stages until the final concentrationof 45% is attained in the last stage in which the crystallization zonetemperature will range between from 5 C. to 6" C. The slurry in eachstage contains from about 20% to 40% ice; the temperature of each stageis adjusted to optimum crystallization temperature commensurate with thefreezing point of the extract, as herein prescribed; the moreconcentrated extract of each stage is centrifuged before transfer to thenext succeeding stage; and the Wash water of each stage recycled throughthe same or an earlier stage.

EXAMPLE III Orange juice, concentrated for use in preparing frozenjuice, is prepared by squeezing oranges followed by customary separationof the pulp and concentrating the juice by the following process. Theexpressed juice containing about 12% solids, as feed, is chilled toabout C., is passed through inlet (1) FIG. I into a slurry containingfrom 20% to 40% ice and about 40% solution of orange juice and theresulting slurry subjected to subcooling below the freezing point of thesolution, i.e. to about 8 C. The subcooling is effected in the boundaryfilm extract and the extract transferred by turbulence from the boundarylayer to the crystallizer for release of the subcooling by crystalgrowth on the crystals in the slurry. The concentrated extract isseparated by centrifuging; the crystals washed with dilute orange juiceand the resulting wash water returned to the crystallizer with the feed.

The process of the invention is used to freeze ice from an extract, toutilize concurrently the phase change by means of which water in theform of ice is withdrawn from the extract leaving a concentrate (ormother liquor) and thereafter to separate the ice from the concentrate.Indirect heat exchange of the art produces, as we have seen, icebuild-up on heat exchange surfaces that are in contact with the extract.Applicant has discovered that a combination of factors is important inorder to maintain high equipment capacity, to insure continuousoperation, and to sustain relatively high temperature differencesbetween the cooling medium and the extract being concentrated. Moreover,the process restricts ice formation exclusively to crystal growth onfree, i.e., ambulatory nuclei, thus avoiding build-up on heat transfersurfaces. The combination of factors include:

(1) The liquid extract film in immediate contact with the heattransmission surface in the freezing zone is subjected to a relativelyhigh degree of subcooling i.e. 3 to 8 C. or more below solution freezingpoint. During 6 contact the potential ice formation in the form ofnuclei is maximum. Even a slight deposit of ice on the heat transfercooling surfaces cannot be tolerated and by rotating the agitators andreversing their vertical travel at respectively sufiicient r.p.m. andrates deposition is avoided.

(2) The ice crystal concentration in the crystallization zones ismaintained between about 15% and 40% by Weight. This concentration isrequired in order to give a high growth rate of the ice and to insurethat sub-cooling is released on crystals in that zone and that theformation of new crystals, or nuclei, are confined to that zone and tothe crystals in that zone.

(3) The total volume of crystals available for crystallization withinthe freezing zone is sufiicient to reduce substantially the supercoolingwithin the zone and to maintain the supercooling within 1 C. andpreferably les than 0.5 C. below the freezing point of the extract whichmay be at a temperature as low as 15 C. or lower depending on the kindof extract being frozen. This is achieved by using from 50 to 00 gals.of slurry volume for 1000 lbs. of crystals produced per hour. About 200gals. of volume is provided within the freezing zone per 1000 lbs. ofcrystals produced per hour for solution of medium viscosity.

(4) The freezing, or heat transfer, surfaces are preferably highlypolished and are made of a non-corrosive material such for example, asstainless steel or silver, or are silver lined metal surfaces.

(5) Optimum operation involves effective motion in the extract andslurry to sub-cool the extract in the boundary film, to withdraw thesub-cooled uncrystallized extract from the boundary film, to associatethe subcooled film with crystals in the slurry of the crystallizer and'out of contact with the heat transfer zone, and to permit ample timefor release of the sub-cooling as crystal growth. These functions ashave been herein stated are executed by the turbulence in the boundaryfilm, by transporting the sub-cooled extract from the film to thecrystallizing zone and by maintaining a spacially and temporallyconstant state in the latter zone until the sub-cooling has beenreleased. Action of the agitators and especially their reversal ofdirection, coacting with a moderation of through-put of the slurry,controls the duration of the extract boundary layer contact time andalso the state and association of the sub-cooled extract with thecrystals in the slurry to complete release of the sub-cooling. Optimumresults with continuous operation of the process is thus effected.

Applicant has found that boundary film turbulence can be provided invarious ways, for example, by reversing the direction of motion of thepropellers such as in a partial or complete clockwise, followed by likecounterclockwise rotation of the shaft and attached propellers; theclockwise, counterclockwise cycle being repeated 50 to times per minute.These motions can be augmented by the vertical up/ down motion of theshaft to insure film turbulence and crystallizer constant environment,the through-put (velocity) of the slurry through the crystallizer ineither an upward or downward direction being preferably continuous andmay vary from a few feet per second down to a fraction of a foot persecond.

Not only is it important to have the nuclei present in the crystallizer,outside the boundary film, but also important that the number of nucleiand crystals should be capable of absorbing the sub-cooling and inposition to absorb the heat of crystal formation and of crystal growth.Optimum utilization of the invention involves having the crystalspresent in quantity and sub-cooling at the allowable maximum distributedtemporally and spacially in the crystal forming zone of thecrystallizen-Uniform distribution of crystals in zone 12 is induced by aturbulent state which avoids loci crystallization, i.e., points ofcrystallization as the sharp corners of the equipment, rough surfaces,and other possible crystal forming protuberances of the propellersurfaces. Suitable turbulence to give the spacial (and temporal)requirements in zone 12, as well as in the boundary film, is attained bythe action of the agitators or equivalent means is at least ample,taking into consideration the configuration, size, fluid-solid flow(slurry flow), viscosity of the extract and other essential chemicalengineering factors to provide turbulent state flow velocities (i.e.critical velocities) in the boundary film and in zone 12. By theprovision of crystals within the crystallizer and their uniformdistribution, as well as means for introducing additional crystals atsuitable positions in the crystallizer at any suitable point at whichsurface crystallization might otherwise occur, the ice crystals are heldin suspension throughout zone 12 with substantially free flow throughthe crystallizer.

Crystals introduce-d not only grow within the crystallizing extract byrelease of the heat of sub-cooling but also produce the desired crystalform and habit. The recycled crystals should be compact in density anddiscrete in association in order to be separated readily by centrifugeor other means from the adhering concentrate. The natural tendency isfor water and also extracts to form ice at very rapid rates and to formice as snow-like crystals. Such crystals in contradistinction to thecrystals produced by the process of the invention are neither compact indensity nor discrete in character; and moreover, snowlike crystalsocclude and tenaciously hold and retain undesirable amounts ofconcentrate when such crystals are produced in concentrating extracts.

Discrete ice crystals are produced in accord with the invention bynucleating and growing the crystals under a restricted range oftemperatures. The temperature in the crystallizing extract in zone 12 isheld within a narrow temperature range that is below the freezingtemperature of the concentrating solution. This temperature is below C.and is maintained practically constant at a temperature about 1 to 0.1C. below the freezing point of the particular extract, determined by thesub-cooling in the boundary film (which may be many degrees below thesolution freezing point), other cooling means may be provided. Densecrystals are created by holding the temperature difference between theheat transfer surface and the equilibrium freezing point of the extractsuch that between 300 to 1600 B.t.u. per square foot hour is transferredthrough the heat transfer surface and from the sub-cooled film to zone12.

The form, discretion, and habit of the crystals follow closely theprecision with which the constancy is maintained during crystallization.Compact and dense crystals produced by a temporal and spacially constantenvironment are more readily washed free of concentrated extract. Withoptimum control of the heat transfer surface temperature under thepreferred conditions discrete crystals are produced from aqueousextracts that are hexagonal, are of the ditrigonal-pyramidal class andhave the compact dense form most favorable for washing to recoveradhering concentrate without undue melting of the ice during the washingstep. In the specification and claim by the phrase equilibriumtemperature of the freezing extract is meant the average crystallizationend point of the extract. Optimum capacity is obtained by adjusting theheat flow to decrease the temperature at any one freezing stagecommensurate with the increase in concentration of the extract. Thetemperature decrease is produced by known means such for example as bylowering the pressure on the refrigerant if ammonia or an equivalentvaporizable refrigerant liquid is used or decreasing the temperature ofnon-volatile coolants such as brine or a halogenated hydrocarbon whichis circulated through the cooling jackets.

The process is operated by introducing an extract precooled to atemperature approaching 0 C. into the circulating slurry. Any extract,for example, fruit juices as treated such as: orange, lemon, pear,grape, apple, and guinabana; potable liquors i.e. milk, wine, coffee,beer,

vegetable juices, e.g. tomato, carrot, cabbage, onion, and beet; andother comestible extractions containing potable liquids and alsobrackish and saline water or other organic or inorganic substances.

Multi-efiect or stepwise concentration is indicated in the concentrationof those extracts that are dilute or for those to be dehydrated. Thetemperature in the different effects as well as the number of efi'ectsemployed are dependent on the percentage concentration of the juicedesired in the product concentrate. For example, in the preparation of afinal organge juice concentrate containing 50% solids by weight, andusing three effects, recommended temperatures in zone 12 of thecrystallizers are: first effect minus 3 0.; second effect minus 8 C.;and the third effect minus 12 C. In relatively large installations fouror even more effects can be used. For relatively small production manystages are not usually justified, due to the cost of extra piping andauxiliary equipment required.

The centrifuged discrete crystals are preferably freed from adheringconcentrate by washing with extract feed precooled to a temperaturebelow about 1 C. and/or temperature controlled water which wash waterextract is added to feed to recover extract otherwise retained on thecrystals. The crystals in the slurry should on the one hand besufficient in quantity to provide points of crystallization throughoutzone 12 for release of the heat of crystallization (sub-cooling) in theformation of discrete ice crystals. Too great a quantity of crystalswill result in too many crystals of undesirable size. By restricting thenumber of crystals the sub-cooling will be released in producing largecrystals and not in producing an equivalent weight of small crystals.The number of nuclei should therefore be less than the number that willproduce crystals having an average size of less than about 0.2 mm.,which is the minimum size for efficient handling and washing of thecrystals. Crystals are preferably much larger .5 to .8 mm. or more.

Efiicient concentration of comestible, imbibable, and other extracts bythe process of the invention stems inter alia from the formation duringthe concentration of granular ice crystals having a high bulk density.Water of course will crystallize in the form of snow-like crystalshaving an extremely low bulk density. Snow-like crystals will holdtenaciously any retained extract or concentrated solute. An economicalprocess for the concentration of the solutions described herein isoperated under close tolerance that avoid the formation of snow-likecrystals. Moreover, the sub-cooling is imparted to the extract while theextract is in the boundary film and that sub-cooling released in formingcrystals and growing them in intimate contact with the suspendedcrystals. Furthermore, as crystals are formed and grown theconcentration is carried out under strict control of temperature.Moreover, crystals are produced as discrete particles and are subjectedto crystal growth also under precise control and importantly in thepractical absence of localized heating and cooling effect duerespectively to controlled introduction of the extract and controlleduse of the refrigerant.

The process, apparatus, and conditions described may be modified in manyways within the purview of the invention as herein disclosed and claimedwithout departing from the invention or without operating outside thescope of the claim.

I claim:

Apparatus for the concentration of solute in a solvent bycrystallization of solvent into solid crystal form, comprising:

(1) a crystallizer comprising a cylindrical jacketed heat transfersurface having an inlet portion and an outlet portion;

(2) agitation means comprising a rotatable shaft, adapted for periodicreversal of direction and for oscillation parallel to the axis of saidcylindrical heat transfer surface, provided with a plurality ofagitators extending therefrom, and arrange-d to define an apparatus freezone adjacent said heat transfer surface, and a crystal forming zoneadjacent said apparatus free zone, said agitation means adapted tocreate turbulence in said apparatus free zone so as to keep said heattransfer surface free from solids;

(3) means for feeding solution into said crystallizer through said inletportion; and

(4) means withdrawing crystals in slurry from said out-let portion ofthe crystallizer and returning recycle crystals in liquid slurry forintroduction into said crystallizer inlet portion together with freshsolution.

References Cited UNITED STATES PATENTS Badger 6258 XR Bottoms 62-58 XSchuftan 62-58 Wenzelberger 62-58 Wenzelberger 6258 Benscheidt 62 58Slattery 6258 Thompson 62-58 NORMAN YUDKOFF, Primary Examiner. G. P.HINES, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,328,972 July 4, 1967 Hans Svanoe n the above identified It iscertified that error appears i ted as patent and that said LettersPatent are hereby correc shown below:

Column 1, line 11, beginning with "This" cancel all to and including"3,209,378." in line 14, same column 1, and insert This application is acontinuation-in-part of the Hans Svanoe application Ser. No 235 ,355filed Nov. 5 1962, now U.S. Patent No. 3,285,021, and a continuation ofapplication Ser. No. 297,498, filed July 25, 1963, now

abandoned.

Signed and sealed this 4th day of November 1969.

(SEAL) Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

